Silicon has increasingly been used in optical applications. Currently such optical components as waveguides, beam splitters, detectors, lasers, and the like can all be formed in silicon. Forming such components from silicon enables small high frequency response, lower energy components as well as large scale manufacturing using semiconductor fabrication methods.
Recently, thin silicon oxide layers have been grown on silicon components to form antireflective coatings on silicon in order to achieve a desired light path. In order to function properly, antireflective coatings must have a thickness matched to the wavelength of light used in the optical system. Any variation in the thickness of the antireflective coating can introduce unwanted reflections, attenuation, and other irregularities. Inasmuch as the optical spectrum is from 400 to 700 nanometers, achieving a specified antireflective coating requires extremely accurate manufacturing processes.
Silicon is a face centered cubic (FCC) crystal structure having 100, 110, and 111 plans, and permutations thereof. In the presence of oxygen, oxide layers will grow on facets parallel to the 100 and 111 planes at different rates. Accordingly, two facets on the same substrate that are parallel to the 100 and 111 planes, respectively, will have oxide layers of different thicknesses after having been exposed to oxygen for the same period of time. As a result, the facets will not bear oxide layers suitable for suppressing reflection of light at the same wavelength.
For example, FIG. 1 illustrates a substrate 10 having a faceted upper surface having facets 12a-12c parallel to the 100 plane 14 of the silicon substrate and facets 16a, 16b parallel to the 111 plane 18. For purposes of the disclosure the 100 plane 14 may mean any of the permutations of the 100 planes of an FCC material including the 100, 010, and 001 planes. Other facets formed on the substrate 10 may be parallel to the 110 plane and the 101 and 011 permutations thereof.
The substrate 10 is exposed to an oxidizing environment such that an oxide layer 20 is grown on the silicon substrate 10 will have a thickness 22 on facets 12a-12c that is less than a thickness 24 on facets 16a, 16b due to the faster growth rate of the 111 plane 18. Oxide layers grown on the 110 plane may likewise have a thickness different than the thicknesses 22, 24.
In view of the foregoing it would be an advancement in the art to provide a system and method for growing uniform oxide layers over both the 100 and 111 planes. Such a system and method should be capable of use in large scale manufacturing of silicon optical components.